Replacing Timing Chains: I think I figured out how to avoid retiming cams. Opinions?
 

I am sure you guys are almost as tired of this problem (see this thread: http://forums.pelicanparts.com/porsche-911-technical-forum/105756-wayne-john-walker-help-turns-counter-clockwise-but-not-clockwise.html ) as I am, but I just wanted to run this idea by the experts before I begin.

I have been convinced that I need to install new timing chains as a first measure to try to addess the problem, but I have been trying to avoid retiming the camshafts. While trying to get to sleep last night, I think I came up with a way to replacing the timing chains without redoing the cam timing.

The problem with turning the crank without turning the cams is that the valves hit the pistons. Solution: get the valves out of the way by backing off the rockers. My proposal:

1. Jack up car, pull muffler, rear valance, etc.
2. Disconnect battery and put car in neutral
3. Remove chain box covers and rocker covers.
4. Pull the spark plugs, distributor cap and ignition wires.
5. Turn car to EXACTLY Z1 and check distributor to confirm at #1 firing position (mark this first). Take this opportunity to scribe a reference line on the camshaft relative to some fixed points to be able to confirm that the cams don't move during remaining procedure.
6. Back off all of the rocker arms on valves that are open on passenger side of the car to close these valves and move them out of the way of the pistons.
7. Remove passenger side chain tensioner, compress, and insert retaining pin ready for reinstallation.
8. Break passenger side chain.
9. Tie end of new master link chain to end of old stretched(?)timing chain with small wire ties or wire.
10. Rotate engine to pull chain around the intermediate shaft sprocket until back EXACTLY at Z1 again. Confirm cam didn't move by reference scribe line.
11. Put chain over the cam sprocket and close master link.
12. Reinstall passenger side tensioner.
13. Repeat steps 6-12 except for driver's side of the car.
14. Set valve lash.
15. Button-up, reinstall plugs, wires, distributor cap, connect battery and start.

I think this will work. Do you agree?

Rich

What's stopping you from just retiming the cams? This approach might work, but your measurements would have to be super-critical. Doesn't it make you nervous?

I can't think of any reason that would'nt work, as long as the rotations your talking about end up being 2 full rotations (crankshaft turns 2 times to every camshaft rotation.)

Chuck: You're right. I forgot to say to rotate the engine 720 crank degrees to get back to #1 firing position. That's why I wanted to use the distributor rotor being at #1 to ensure being at #1 firing position. Forgot to explain.

Colin: I guess I'm just chicken (plus I don't have one of those gizmos to hold the dial indicator).

are you going to try to do it without removing the chain housings? don't say you weren't warned. how do you know the cams are even in the right place now? i'm sure pelican has the dial guage holder. just do it right. there's certainly enough info on this site.

John: Yup. I was just planning to tie the new chain to the old chain with small plastic wire tires (i.e. make a temporary nylon plastic link) and turn the crank allowing the chain to guide itself through the depths and back out again.

Ya know the sound it makes when piston meets valve??? CHA-CHING!!!

sounds good in theory...

I'll admit my first cam timing was an ordeal...but once you've done the procedure it really isn't that bad

I actually did it faster and more accurately when I had to redo them with the engine in the car (partial engine drop) tehn when I had the engine out on a pallet

I thik it is one of those procedures that is really really hard to put into words...and if you are tackling it for the first time, you have to start knowing the you'll prob do it 2 or 3 times as practice before you get it totally right....

Personally if your chains are stretched, there is a chance they are mistimed because of the stretch anyways...and it would be a shame to do 3K in damage to your valve train because of 2 hours of labor you didn't want to do

good idea though...now if only you can figure out a way for me to change the intake manifold boots on my CIS without having to take the engine out....

MJ

I cannot imagine that the cams are that far off and the valves are not hitting the pistons. As I said in the other thread, the engine runs well, idles well, and the carburetors draw almost identically on both sides almost right off the bat after being set to a baseline starting position. Maybe I'll do the cam timing too, but it just sounds like a hassle that is not necessary. It is hard enough to find room to work in there much less trying to hold the cam in place while tightening the nut and not moving anything around. Anyhow, it sounds like it should work.

Rich

PS: If you know anyone who is interested in my Daytona Yellow and black 1969 Z/28, it is available for sale. I never thought I would hear myself say that, but I am just not into the restoration thing and I want to have something to take to the track. It is a numbers matching original Z/28 (DZ 302, 4speed, etc.). Engine has some bolt one hop-ups, but could be put stock easily. Original block and heads. Paint is pretty nice but old. Interior is excellent and the car has 58,890 original miles. Send interested parties to my e-mail and I'll provide more details.

Rich

Cam timing is not a hassle. Bent valves are.
There is a great how-to on cam timing in the archives as posted by Sherwood Lee (911pcar). Read it.

Snap out of it Rich!!

Am I missing something here? Wouldn't the new timing chains be slightly different in length (i.e: not stretched) that would make retiming the cams the right way a necessity anyway?

It's been a few years since I timed the cams on my car, but it was really no big deal if you have the right tools.

Jim

Rich: I gather from your other posts, that your not completely new to this sort of thing.

I suspect everybody is being a little conservative here, thinking you don't know what you're doing and your cutting corners (you are however, cutting corners. Remember recheck, recheck, recheck?) I think though you have thought this through and are on to a way of doing something that should work, which I appreciate. With that said, were it me, I would recheck cam timing, but I kind of like doing that sort of thing. But, if you turn the motor over by hand when your done and feel no interference you should be alright. As you probably know this won't be any guaranty that there won't be interference when you run it, but it probably won't be devastating. Good luck.

BTW: A good friend of mine had a 69 Z28 with a 302 solid lifter motor. That was a fun car. I still have kind of a soft spot, but with 2 Porsches, and a boat to take my time, I'm already taxing my wife to the limit, so I don't think I will be buying it.